Many hormones are secreted by neural processes emanating from the brain. Neurons have cell bodies at which electrical excitability is generated. After generation within the cell bodies, electrical impulses are propagated considerable distances along slender extensions called axons. Axons terminate in extensive terminal structures that contain specially packaged chemical substances. The arrival of electrical impulses into nerve terminals triggers the release of the chemical substances. Neurosecretory neurons are a special class of neurons that contain peptide hormones within their terminals and release these hormones into the blood. These hormones then circulate throughout the body and exert a wide variety of effects.
The neurohypophysis (posterior pituitary) consists of nerve terminals that secrete two peptide hormones. One of these hormones, oxytocin, stimulates uterine contractions during childbirth, lactation, and a variety of behavioral responses associated with reproduction. The other hormone, vasopressin (also known as antidiuretic hormone or ADH) stimulates water reabsorption by the kidney, blood pressure increases, and coagulation of blood through platelet aggregation. Controlling these functions can be of great value in medical situations, including conditions associated with or brought about by inappropriate, improperly regulated, or abnormal peptide hormone release. For example, premature labor is often associated with inappropriate oxytocin secretion. Swelling, edema, and bloating are often related to excessive vasopressin secretion. Risk of heart disease and heart conditions may also be increased by excessive vasopressin secretion.